Hectograph products and process

ABSTRACT

Novel thixotropic hectograph printing ink and process for printing hectograph master sheets or transfer sheets therewith comprising preparing a semi-solid, thixotropic hectograph printing ink containing non-drying semi-solid oleaginous material, film-forming binder material at least partially dissolved in a relatively high boiling organic solvent having dispersed therein hectograph dyestuff and finely-divided fusible, waxy particles, printing the hectograph composition in image form onto a master sheet or as a continuous or spot layer on a foundation and heating such as by means of infrared radiation to heat the composition to a temperature above the melting point of the waxy particles to fuse the composition and render it smooth, smear-resistant and stable.

This application is a continuation-in-part of parent application Ser.No. 312,736, filed Dec. 6, 1972 now abandoned.

The most conventional hectograph compositions are applied as hot-meltwax compositions or resinous solvent compositions to formpressure-sensitive hectograph transfer sheets carrying a layer of waxand/or resin composition containing undissolved hectograph dyestuffwhich is transferable in image form to a master sheet under the effectsof writing or typing pressure. The images formed on the master sheet arerelatively soft and contain exposed dye crystals and/or dye-dissolvingoils and cannot be handled or rubbed without dislodging portions of thedyestuff but this generally is no problem because the imaged master isusually used immediately in the spirit duplicating process and thendiscarded.

It is also known to print hectograph masters directly, such as by crashimprinting, using a hectograph printing ink comprising a hot-melt waxcomposition containing undissolved dyestuff. The images printed withsuch compositions are relatively soft and smear during handling or as aresult of abrasion against contacting sheets, such as when such printedmasters are bound in book form for school use. Also, with crashprinting, it is only possible to print images and it is not possible toprint large areas such as required for the production of transfer sheetssuch as spot carbons and full carbons.

It is the principal object of the present invention to provide printedhectograph compositions, such as images and transfer layers, which arecleaner to the touch and more abrasion-resistant and stable then priorknown hectograph compositions.

It is another object of this invention to provide hectograph printinginks which are capable of being printed onto a master sheet in the "silkscreen" printing process to provide smooth hectograph images which haveimproved rub-resistance and bleed-resistance and provide a large numberof intense copies in the spirit duplicating process.

It is another object of this invention to provide a novel printingmethod for improving the cleanliness, rub-resistance and copy capacityof hectograph compositions printed from a hectograph printing ink.

It is another object of this invention to provide a novel ink system forthe silk screen process in which the ink is solvent-dispersible and thuscan easily be cleaned from a screen after use.

These and other objects and advantages of the present invention will beapparent to those skilled in the art in the light of this disclosureincluding the drawing, in which:

FIG. 1 is a diagrammatic cross-section, to an enlarged scale, of amaster sheet being imaged with hectograph printing ink through a stencilsheet, the sheets being shown out of contact for purposes ofillustration, and

FIG. 2 is a diagrammatic cross-section, to an enlarged scale, of amaster sheet carrying printed hectograph images which have been fused bymeans of infrared radiation.

The objects and advantages of the present invention are accomplishedthrough the use of novel hectograph printing ink compositions and by thenovel process of fusing the hectograph images which have been printedonto the master sheet.

The silk screen printing process is a generic name for a stencilprinting process employing an ink-permeable screen which may be of silk,nylon, polyester, stainless steel or other monofilament or polyfilamentthread construction. Portions of the screen are treated or masked torender them impermeable to ink to provide a stencil in which theremaining ink-permeable areas correspond to the images or areas to beprinted. The stencil screen is placed above and closely spaced from acopy sheet and the printing ink is drawn across the top of the screen,such as by means of a squeegee, to force the stencil sheet against thecopy and squeeze the ink through the ink-permeable areas and onto thecopy sheet. The printed copy sheet is dried by evaporation of thevolatile vehicle. The process can be repeated with a number of freshsheets to produce a number of copies from the same stencil screen byrepeating the inking step.

Conventional screen printing inks are prepared by grinding stronginsoluble pigments into a vehicle composed of dehydrated castor oil,synthetic resin, boiled linseed oil and solvent such as kerosene orsolvent naphtha to provide a short ink which will run over the screeneasily and will permit easy separation of the screen and the printedcopy.

The novel hectograph printing ink compositions of the present inventioncomprise from about 30% to 80% by weight of volatile organic liquidvehicle having a boiling point above about 200° F. and from 20% to 70%by weight of solids, some of which are dissolved and some of which aredispersed in the vehicle. The solids comprise hectograph dyestuff, hardwaxy material having a melting point above 140° F., film-forming bindermaterial, non-drying oleaginous material and, preferably, an infraredradiation-absorbing material.

The volatile organic solvent vehicle of the printing ink consists of oneor more liquids of relatively low volatility, such as naphtha, mineralspirits, kerosene, toluene, xylene, or the like, having boiling pointsof between about 200° F. and 460° F.

The hectograph dyestuff, which preferably comprises from more than about50% by weight up to about 85% by weight of the solids content, ispresent in the ink in the form of fine dispersed crystals, with a smallportion being incidentally dissolved by the vehicle. Suitable dyestuffsinclude all of the conventional spirit-soluble hectograph dyestuffs suchas crystal violet, methyl violet, Malachite green, and the like, as wellas the conventional spirit-soluble, substantially colorlesscolor-forming materials such as crystal violet lactone and other colorprecursors which react with a complementary color-forming materialpresent in the duplicating fluid or on the copy sheets to form coloredimages.

The binder material of the hectograph ink comprises a combination of aminor amount by weight of a film-forming material, which is at leastpartially soluble in the system so as to impart viscosity to the ink,and a major amount by weight of one or more hard waxy materials whichare dispersed in finely-divided particulate form in the ink system. Thefilm-forming material preferably comprises from about 2% to about 15% byweight of the solids content and preferably is a cellulosic materialsuch as ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethylcellulose, or the like, but other suitable film-formers may be selecteddepending upon the solvent system selected (e.g. for fast or slowdrying, etc.). The finely-dispersed hard waxy material may comprise fromabout 5% up to about 20% by weight of the solids content and preferablyis carnauba wax, although other hard waxes such as montan wax, hardmicrocrystalline wax, ouricury wax and other waxy materials having amelting point above about 140° F. and below about 300° F. are alsosuitable, such as polyethylene, silicone gums, and the like.

The present compositions also comprise from about 5% by weight up toabout 20% by weight of a non-drying semi-solid oleaginous material whichmay be soluble or insoluble in the volatile vehicle and which is atleast partially incompatible with the hard wax in the cold. Theoleaginous material preferably is a semi-solid material having a meltingpoint below about 185° F. so as not to bleed from the hectographcomposition after printing. Among the suitable semi-solid oleaginousmaterials are animal fats such as lanolin and lard, soft mineral waxessuch as petrolatum and Bareco Micro Pet Amber B, hydrogenated vegetableoils such as hydrogenated castor oil, fatty acid esters such as themethyl ester of 12-hydroxy stearic acid, and the like. All of thesesuitable materials are soft solids at ordinary room temperatures, i.e.about 75° F., and liquefy at a temperature below about 185° F. Liquidoils and plasticizers may be used in combination with the semi-solidmaterial, such as mineral oil, animal oils such as lard oil, butylstearate, and the like, provided that they do not dissolve the dyestuffto any substantial degree and are present in lesser amounts than thesemi-solid material and are compatible therewith so as to formnon-flowable mixtures.

The oleaginous material functions to increase the amount of dyestuffwhich can be leached from the hectograph images in the spiritduplicating process. Thus it retards the formation of a hardened tar orcrust of the dyestuff at the surface of the images during theduplicating process, which tar or crust tends to be formed when a largeamount of dyestuff is exposed to the spirit duplicating fluid. Such atar or crust of dye has poor solubility in the spirit fluid and producesfewer and less intense copies. The oleaginous material is at leastpartially incompatible with the waxy material in the amounts used, andseparates therefrom after fusion to provide a heterogeneous combinationof waxy material and oleaginous material at the surface of and withinthe fused images. This structure permits the dyestuff to be dissolvedgradually from the images, preventing tarring, and providing a largenumber of intensely colored spirit copies. The master images are cleanto the touch because the oleaginous material preferably is substantiallya non-solvent for the dyestuff and thus is free of dyestuff. Since theoleaginous material is a semi-solid material, it may be capable ofdissolving some small amount of the dyestuff and will still providerelatively clean images because the semi-solid material is not fluid andwill not exude from the images to stain the hands or form dye-containinghalos on the master sheet.

According to a preferred embodiment, the present hectograph inkcompositions contain a material capable of absorbing substantial amountsof infrared radiation. Such material may be a conventional black pigmentsuch as a carbon black dispersed in the ink, or a conventionalinfrared-absorbing compound, commercially available for the purpose,dissolved or dispersed in the ink. Suitable amounts vary with theeffectiveness of the material. Carbon black or similar black pigment maybe used in an amount ranging from about 0.5% up to about 5% by weight ofthe solids content. Commerically available infrared absorbers areeffective in smaller amounts down to about 0.1% by weight but areexpensive.

Basically the present hectograph ink compositions are thixotropiccompositions which are semi-solid and only slowly-flowable, if at allflowable, at ordinary room temperatures, but which flow readily whenmoved, and comprise a dispersion of wax particles and hectographdyestuff in a volatile organic vehicle containing a semi-solidoleaginous material, which is at least partially incompatible with thewax, and a film-forming binder material. The present compositions have asolids content of between about 20% and 70% and the dispersed materials,namely wax and dye and possibly carbon black, are sufficiently fine topass through the openings of a conventional silk screen stencil, i.e.smaller than about 10 microns for the wider mesh screens and preferablysmaller than about 5 microns for screens down to about 250 mesh. Thisthixotropic, semi-solid ink is relatively stable at room temperatures,will not flow in the absence of applied motion, will not rapidly dry inthe absence of applied heat, will not harden on the silk screen orstencil and will not clog or plug the openings therein, and will notflow on the master sheet.

One embodiment of the present process is carried out in the mannerillustrated by the drawings whereby a stencil sheet 10, such as a silkscreen 11 covered by an impervious masking layer 12 except in open areas13 corresponding to the images to be copied, is positioned against aconventional master sheet 20. An infrared radiation-absorbingthixotropic hectograph ink composition 14 is drawn across the barrierlayer 12 by means of a conventional squeegee 15 whereby portions 16 ofthe ink are forced into open areas 13, through the silk screen 11 andagainst the surface of the master 20 to form printed ink images 21thereon corresponding to the open areas of the stencil sheet 10.

Next the stencil sheet 10 is carefully separated from the master sheet20 carrying ink images 21 and the latter is exposed to light sources 40rich in infrared radiation and preferably to a flow of warm air. The inkimages 21 selectively absorb the infrared radiation while the mastersheet 20, such as white paper, does not absorb the radiation to anysubstantial extent.

As shown by FIG. 2, the final imaged master sheet 30 comprises fusedhectograph images 31.

The use of infrared radiation-absorbing compositions, in associationwith the use of infrared radiation to cause fusion of the printedimages, is a preferred embodiment of the present invention. The heatingof the printed images accomplishes not only the evaporation of thevolatile vehicle but also the melting and coalescence of the hard waxparticles and the plasticizing of the wax by means of the oleaginousmaterial. The images are heated above the melting point of the waxymaterial, but the images do not flow or spread during fusion because themaster sheet itself is not heated by the infrared radiation. This isimportant because any spreading or broadening of the master images iscompounded on each of the duplicate copies produced from the master inthe spirit duplicating process.

However, it is also possible to dry and fuse the present hectographimages or compositions by other conventional means such as a hot plateand/or by heated air provided that the heating is carefully controlledin order to prevent excess melting and spreading of the images orcomposition being dried.

The printed images 21, shown in FIG. 1, comprise the wax particles anddye crystals held together by means of the film-forming binder material.At this stage the imaged master sheet could be dried at non-fusiontemperatures and used in the spirit duplicating process to producesuitable copies. However the master images have a rough particulatesurface and smear and transfer easily if contacted by the hands or by acontacting sheet. This disadvantage is overcome by the fusion dryingtechnique which converts the printed images 21 into fused images 31. Inthe fused images 31 the waxy particles have been melted or coalescedtogether with the oleaginous material and the dye crystals to form acomposition from which the oleaginous material will not bleed and whichreleases the dyestuff more gradually and evenly in the spiritduplicating process.

Furthermore the fused images 31 have smooth, abrasion-resistant surfaceswhich, apparently due to the presence of fused wax thereover, can behandled and used in book form with a minimum of dye transfer to thehands or to the rear surface of the next contacting sheet in the book.

The following examples are given as illustrations of suitablecompositions and processes encompassed by the present invention.

EXAMPLE 1

The following hectograph printing ink composition is formulated andmixed as discussed below:

    ______________________________________                                        Ingredients          Parts by Weight                                          ______________________________________                                        Carnauba wax         14                                                       Lanolin              15                                                       Statex carbon black  2                                                        Crystal violet dye particles                                                                       150                                                      Ethyl hydroxyethyl cellulose                                                                       7                                                        Naphtha (Amsco 460)  180                                                      Xylene               25                                                       ______________________________________                                    

The carnauba wax may be introduced as particles formed by grinding solidcarnauba wax alone or together with a portion of the naphtha vehicle.Then the carnauba wax particles, lanolin, and 160 parts of the naphthaare heated together, preferably to about 140° F., to form a clear-meltsolution to which the dye and carbon black are added. The cellulosebinder, xylene and remaining 20 parts of the naphtha are mixed togetherto form a solution of the binder, which solution is then milled with thecooled dye dispersion to form a printable thixotropic hectograph inkhaving a smooth texture.

The gradual cooling of the heated wax solution causes the wax to comeout of solution in the form of tiny wax particles or crystals which mayinclude an amount of the oleaginous material as softener and which haveparticle sizes below about 10 microns and preferably below about 5microns as is controlled by the speed of cooling. The dye crystalsremain substantially completely insoluble in the vehicle even at theelevated temperature.

A stencil 10 comprising a negative mask 12 of the desired subjectmatter, in which the openings 13 comprise mirror-reverses of the desiredsubject matter, is positioned against the surface of a master sheet 20and the hectograph ink composition 14 is applied to an impervious edgeof the mask and is drawn across the mask by a conventional squeegee 15having a flexible rubber blade with a straight edge of sufficient lengthto sweep the full length or width of the stencil. This forces the inkthrough the openings 13 and onto the surface of the master sheet 20 inthe form of mirror-reverse images 21 of the ink composition.

Next the thus-imaged master sheet is separated from the stencil sheet,and a succession of fresh master sheets can be positioned against thesame stencil and imaged in the same manner to produce duplicate mastersheets, if desired, since the ink vehicle has a low volatility and theink will not dry on the silk screen and plug it.

Each printed master sheet is immediately placed under the influence ofinfrared radiation or heat to evaporate the volatile naphtha and xyleneand fuse the meltable waxy particles to form the final master sheetcarrying fused hectograph images 31. Images 31 are sharp and clear, freeof halos, smooth and relatively clean to the touch, and capable ofproducing excellent copies in the spirit duplicating process.

EXAMPLE 2

The following ink formulation is formulated and mixed as discussedbelow:

    ______________________________________                                        Ingredients          Parts by Weight                                          ______________________________________                                        Carnauba wax         15                                                       Lanolin              15                                                       Mineral oil          10                                                       Peerless carbon black                                                                              3                                                        Crystal violet dye particles                                                                       120                                                      Ethyl cellulose      15                                                       Xylene               30                                                       Mineral spirits      145                                                      ______________________________________                                    

The carnauba wax is mixed, preferably at elevated temperatures, with thelanolin and mineral oil and added to the major amount of the volatilevehicle mixture containing the dye and carbon black, causing the wax toreach a dispersed phase on cooling. The cellulose binder is separatelydissolved in the remainder of the solvent mixture and the bindersolution and cooled dye dispersion are milled together to form aprintable, semi-solid hectograph ink composition which is printed andfused in the manner outlined in Example 1 to produce similar excellentmaster sheets.

The ink compositions of the present invention are particularly adaptedfor use in the "silk screen" printing process, using conventionalscreens such as those having 180 or 160 lines per inch but coarser orfiner meshes may be used. However other open stencils can be usedinstead of silk screens, where appropriate, and if desired the presentinks can be printed directly using relief or intaglio printing plates.

The present thixotropic hectograph ink compositions are unique withrespect to their resistance to forming dye-containing halos on themaster sheet due to the fact that the fused images are substantiallyfree of dissolved dye and of flowable oils. For this reason the presentmaster sheets preferably are transparent or sufficiently translucentthat the mirror-reverse hectograph images on the face of the master canbe proofread through the back of the master. This alleviates thenecessity of applying corresponding direct-reading images on the back ofthe master. Furthermore an imaged transparent plastic film master can beused as a projection transparency to project the hectograph images assharp, clear images devoid of the dyed halos which accompany priorhectograph compositions containing liquid dye solvents such as castoroil. The present images also are resistant to melting under the heatgenerated by the projection lamp whereas prior hot-melt wax compositionscontain lower melting waxes and melt and spread when exposed to aprojection lamp for a few minutes.

It is noted that impermeable master sheets and foundations, such asplastic films, can be used according to the present invention becausethe present compositions set by fusion whereas prior hot-melt andsolvent compositions set by cooling or evaporation of the solvent and,to an important extent, by absorption of a portion of the oils and/orvolatile solvent by the foundation. Thus prior hectograph compositionsadhere better to paper than to plastic film whereas the presentcompositions adhere equally well to plastic film.

A further advantage of the present hectograph compositions which includean infrared radiation-absorbing material is that such compositionsprovide imaged master sheets which are thermographically-reproducible bymeans of the conventional infrared radiation copying systems. Mostimaged hectograph master sheets are not thermographically-reproduciblesince such compositions are substantially free of materials capable ofabsorbing substantial amounts of infrared radiation. This advantage isquite important where the present master sheets are used in book formfor educational purposes and where one or more thermal copies may bedesired for record purposes.

According to another embodiment, the present hectograph ink compositionscan be printed onto a web to form full or spot carbons since the fusedcomposition, while resistant to spreading during ordinary handling, ispressure-transferable. Thus the composition may be applied to a full orsectional printing roller in conventional manner, printed onto a web ofpaper or plastic film and exposed to infrared radiation to evaporate thevolatile vehicle and fuse the wax particles. The fused composition isexcellent for spot carbon use because the composition can be printed andfused to provide sharp, clean spot hectograph applications which willnot bleed dyestuff onto adjacent areas of the foundation and whichresist staining adjacent sheets in the absence of applied imagingpressure.

However it is preferred to apply a conventional tacky supercoating overthe transfer layer in order to improve its frangibility and its bondingproperties with respect to a copy sheet. The supercoating, which may becoated but preferably is printed over the hectograph composition, may bea hot-melt wax composition comprising a tacky wax such as paraffinand/or a tacky resin such as polyisobutylene.

While most of the present compositions are thixotropic because of thenature and proportions of the basic ingredients, as is the case with thecompositions of Examples 1 and 2 hereof, it is sometimes necessary inthe case of compositions containing a high amount of the volatilesolvent, i.e. 70% to 80% by weight, to include a conventional thickeningagent such as a fumed microporous silica available under the trademarkCab-o-sil or a treated bentonite clay useful in organic solvent systemsand available under the trademark Bentone. Generally an amount equal tofrom 1% to 5% of the total weight of the composition is sufficient torender the composition thixotropic provided the other ingredients arepresent in the specified amounts.

While it is preferred to produce the present compositions by dissolvingthe hard wax together with the semi-solid ingredient and the oil, ifpresent, at elevated temperatures and then causing the hard wax toprecipitate out of solution on cooling when the wax solution is mixedwith the bulk of the solvent and the dye, it is also possible to producethe present compositions in the cold by milling the hard wax and otheringredients in the volatile solvent to reduce the wax to the desiredparticle size.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

We claim:
 1. Thixotropic semi-solid hectograph printing ink which issubstantially free of dissolved hectograph coloring matter comprisingfrom about 30% to 80% by weight of a liquid vehicle consisting of atleast one volatile organic liquid vehicle having a boiling point betweenabout 200° F and 460° F and having a solids content of from about 70% to20% by weight comprising:a. from about 50% to 85% by weight of thesolids content of dispersed, finely-divided, undissolved spirit-solublehectograph coloring matter which is substantially completely insolublein said liquid vehicle, b. from about 5% to 20% by weight of the solidscontent of dispersed, finely-divided, hard wax particles having amelting temperature between about 140° F and 300° F, c. from about 2% to15% by weight of the solid content of film-forming binder material whichis at least partially soluble in said liquid vehicle, the weight of saidfilm-forming binder material present being less than the weight of saidhard wax particles present in said ink, and d. from about 5% to 20% byweight of the solids content of a non-drying, semi-solid, oleaginousmaterial which is at least partially incompatible with the hard wax andwhich has a melting point below about 185° F, substantially all of thedispersed solids in said ink being less than 10 microns in size and saidink being capable of being printed and dried and fused at elevatedtemperatures to provide a clean, rub-resistant, stable duplicatingcomposition.
 2. Hectograph printing ink according to claim 1 in whichthe solid content comprises from about 0.1% to 5% by weight of amaterial capable of absorbing substantial amounts of infrared radiation.3. Hectograph printing ink according to claim 1 comprising naphthavehicle, hectograph dyestuff, carnauba wax particles, cellulosic bindermaterial and lanolin.
 4. Process for preparing thixotropic, semi-solidhectograph printing ink which is substantially free of dissolvedhectograph coloring matter and which is capable of being printed anddried and fused at elevated temperatures to provide a clean,rub-resistant, stable duplicating composition comprising the steps of:a.preparing a dispersion of from about 5% to 20% by weight, based upon thetotal solid content, or hard wax particles having a melting temperaturebetween about 140° F and 300° in a liquid vehicle consisting of avolatile organic liquid vehicle having a boiling point between 200° Fand 460° F, said vehicle containing from about 5% to 20% by weight,based upon the total solids content, of a non-drying semi-solid,oleaginous material which is at least partially incompatible with saidand has a melting point below about 185° F, b. mixing from about 50% to90% by weight, based upon the total solids content, of finely-dividedsolid particulate spirit-soluble hectograph coloring matter, which issubstantially insoluble in said volatile organic liquid vehicle, withsaid dispersion, c. preparing at least a partial solution of from about2% to 15% by weight, based upon the total solids content, offilm-forming binder material in a volatile organic liquid which has aboiling point between about 200° F and 460° F and which is miscible withthe organic liquid of said mixture and is a non-solvent for saidhectograph coloring matter, and d. milling said mixture of step (b) withsaid solution of step (c) to form said ink containing from 30% to 80% byweight of said organic liquid and having a solids content of from about70% to 20% by weight and in which substantially all of the dispersedsolids are less than 10 microns in size and which contains a largeramount by weight of sad hard wax particles than of said film-formingbinder material.
 5. Process according to claim 4 in which saiddispersion of step (a) is formed by heating the hard wax in said vehiclecontaining said semi-solid oleaginous material to form a clear liquidand then cooling said liquid to cause the hard wax to come out ofsolution in the form of finely-divided dispersed particles in saidvolatile organic vehicle.
 6. Process for printing a hectograph imagingcomposition in image form onto a master sheet comprising the steps of:A. providing a thixotropic semi-solid hectograph printing ink which issubstantially free of dissolved hectograph coloring matter comprisingfrom about 30% to 80% by weight of a liquid vehicle consisting of atleast one volatile organic liquid vehicle having a boiling point betweenabout 200° F and 460° F and having a solids content of from about 70% to20% by weight comprising: a. from about 50% to 85% by weight of thesolid content of dispersed, finely-divided, undissolved spirit-solublehectograph coloring matter which is substantially completely insolublein said liquid vehicle, b. from about 5% to 20% by weight of the solidscontent of dispersed, finely-divided, hard wax particles having amelting temperature between about 140° F and 300° F, c. from about 2% to15% by weight of the solids content of film-forming binder materialwhich is at least partially soluble in said liquid vehicle, the weightof said film-forming binder material present being less than the weightof said hard wax particles present in said ink, and d. from about 5% to20% by weight of the solids content of a non-drying, semi-solid,oleaginous material which is at least partially incompatible with thehard wax and which has a melting point below about 185° F, substantiallyall of the dispersed solids in said ink being less than 10 microns insize and said ink being capable of being printed and dried and fused atelevated temperatures to provide a clean, rub-resistant, stableduplicating composition, B. printing said hectograph printing inkthrough an imaged stencil sheet having image wise openings therein ontothe surface of a flexible master sheet foundation to form printed imagesthereon, and C. heating said printed images to evaporate the liquidvehicle and fuse the waxy particles to form dry, smooth images which aresharp, clean to the touch, rub-resistant and stable.
 7. Processaccording to claim 6 in which the ink comprises a material capable ofabsorbing high amounts of infrared radiation, and heating of the printedink is effected by exposure to radiation rich in infrared.
 8. Processaccording to claim 6 in which the solids content of the printing inkcomprises a major amount by weight of hectograph dyestuff and minoramounts by weight of carnauba wax, semi-solid oleaginous material andcellulosic film-forming binder material.
 9. Process according to claim 6in which the master sheet is sufficiently translucent that the imagescan be read through the master sheet.